1. Field of the Invention
The present invention relates to an image reading apparatus and more particularly to an image reading apparatus capable of reading an original such as a document or a photograph, executing conversion into digital data and outputting the obtained image data, and adapted for use for computer input.
2. Related Background Art
At first there will be explained a conventional image reading apparatus with reference to the accompanying drawings. FIG. 13 is a schematic view showing the configuration of a color image reading apparatus, and FIGS. 14A and 14B are respectively a plan view and a cross-sectional view of the conventional image reading apparatus, in which same or equivalent components are represented by a same number.
In the conventional image reading apparatus, as shown in FIG. 13, an original P is placed on an original mounting glass 100 supported by a cover 111 and an original cover 112 is then closed to press the original P to the original mounting glass 100.
Then a reading unit 101 shown in FIGS. 14A and 14B performs a scanning motion parallel to the original mounting glass 100 to read the image on the original P.
The reading unit 101 is provided therein with LED's of three colors (R, G and B) constituting light sources for illuminating the original, an image sensor and a rod lens array for focusing the light reflected from the original P onto the photosensor elements of the image sensor.
The light sources of three colors are turned on in succession and the image sensor reads the light of respective color reflected from the original P to execute color-separated image reading.
In the conventional image reading apparatus, as shown in FIG. 14A, the reading unit 101 is fixed to and supported by a slider 102 which is rendered slidable on a guide shaft 103 fixed to the main body of the apparatus.
Also a belt 104 for transmitting the driving power from a motor 105, constituting scanning drive source, is fixed to the slider 102.
The reading unit 101 is rendered capable of reciprocating scanning motion within a range of the original mounting glass 100 by the forward and reverse rotation of the motor 105. In this operation, the load torque T on the motor shaft can be simply represented as follows:T=F×D/2×i×1/ηwherein F: load in the axial direction, D: diameter of final pulley, i: reducing ratio, and η: mechanical efficiency, so that the load torque T is dependent on the changing ratio.
In case of using flat gears as in the conventional configuration, the changing ratio is represented by the ratio of teeth of the changing gears, and such ratio is generally selected within a range of about 0.1 to 0.3 because of the limitation in the external dimension of the image reading apparatus.
For driving such apparatus, there is generally required a motor of a diameter of 40φ.
As shown in FIGS. 14A and 14B, the image reading apparatus is also provided, as a constituent component, with an electric unit 106 consisting of a control board, a power source etc. These components are housed in a cover 111 supporting the original mounting glass 100.
The above-described conventional technology is however associated with a drawback that the reduction in the dimension and thickness of the image reading apparatus is difficult to achieve.
For example, in the prior technology shown in FIGS. 13, 14A and 14B, in order to reduce the size (height in particular) of the image reading apparatus, the electric unit 106 including a driving system for driving the reading unit 101 and a control board for controlling the entire image reading apparatus is positioned outside the scanning area of the reading unit 101.
Consequently the dimension of the apparatus is reduced in the height, but the longitudinal or transversal dimension becomes larger than the scanning area by the size of the driving system and of the control board. If the electric unit 106 is positioned inside the scanning area of the reading unit 101, the height of the apparatus inevitably increases in order to avoid the interference between the electric unit 106 and the reading unit 101.
It is therefore conceivable to remove the power source, which is bulky in thickness, from the electric unit 106 and receive the electric power for driving the apparatus from an external equipment such as a personal computer thereby only positioning the control board within the scanning area. As the component parts of the power source are bulky, the removal thereof is effective for reducing the height of the apparatus.
However, the thickness of the control board also becomes a barrier for further reducing the height of the apparatus, since a protrusion is more or less present on the bottom face of the reading unit 101 and interferes with the control board.
Though it is possible to reduce the thickness of the control board by replacing all the components mounted on the control board with surface mounted components, there will inevitably result a significant increase in the cost.
It is also possible to suppress the height of the control board by mounting parts requiring a relatively large dimension in the height, such as electrolytic capacitors, in a flatly lying position, but there is required a certain clearance between the control board and a cover therefor in consideration of the bending of the two.
Furthermore, the compactization is inevitably limited since there is required a certain clearance to the scanning member.